Invasive medical device with position sensing and display

ABSTRACT

Apparatus for performing a medical procedure on a tissue within a body of a subject includes a wireless tag configured to be fixed to the tissue and adapted to emit radiation, thereby causing first signals to be generated indicative of a location of the tag in the body. An invasive medical tool includes a probe, which is adapted to penetrate into the body so as to reach the tissue. A handle is fixed proximally to the probe, for manipulation by an operator of the tool. A display, mounted on the handle, presents a visual indication to the operator of an orientation of the probe relative to the tag. A processing unit processes the first signals so as to determine coordinates of the tag relative to the probe, and drives the display responsive to the coordinates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/029,595, filed Dec. 21, 2001, which is acontinuation-in-part of U.S. patent application Ser. No. 09/265,715,filed Mar. 11, 1999. This application is also related to two other U.S.patent applications, filed on even date, entitled “Guidance of InvasiveMedical Procedures Using Implantable Tags,” and “Position Sensing Systemwith Integral Location Pad and Position Display.” All these relatedapplications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to systems for determining theposition of an object inside a human body, and specifically to the useof such systems in guiding tools and other devices used in medicalprocedures.

BACKGROUND OF THE INVENTION

The use of implanted markers or clips for surgical guidance is known inthe art. For example, upon identifying a suspicious lesion in thebreast, a radiologist may mark the location by inserting a simpleradio-opaque wire at the location of the lesion while viewing an imageof the breast under mammography. When a biopsy is subsequentlyperformed, the surgeon follows the wire to find the exact location ofthe lesion, so as to be certain of removing tissue from the correct areaof the breast. Radiologists currently use this sort of location markingfor approximately 40% of all breast biopsies. This careful approachsignificantly reduces the occurrence of false negative biopsy findingsand increases the overall diagnostic accuracy of the procedure.

Despite the proven usefulness of such simple biopsy markers, it would bepreferable for the surgeon to be able to choose a pathway to the biopsysite independently, rather than having to follow the wire inserted bythe radiologist. Furthermore, wire-based markers are not appropriate toother invasive procedures, such as lung biopsies, or to applications inwhich a marker must be left in the body for extended periods. It hastherefore been suggested to use a wireless emitter, or “tag,” to marktarget locations in the body for surgery and therapy. Such a tagcontains no internal power source, but is rather actuated by an externalenergy field, typically applied from outside the body. The tag thenemits ultrasonic or electromagnetic energy, which is detected byantennas or other sensors outside the body. The detected signals may beused to determine position coordinates of the tag. Passive ultrasonicreflectors are one simple example of such tags. Other passive tagsreceive and re-emit electromagnetic radiation, typically with afrequency and/or phase shift. Hybrid tags, combining ultrasonic andelectromagnetic interactions, are also known in the art.

For example, U.S. Pat. No. 6,026,818, to Blair et al., whose disclosureis incorporated herein by reference, describes a method and device forthe detection of unwanted objects in surgical sites, based on amedically inert detection tag which is affixed to objects such asmedical sponges or other items used in body cavities during surgery. Thedetection tag contains a single signal emitter, such as a miniatureferrite rod and coil and capacitor element embedded therein.Alternatively, the tag includes a flexible thread composed of a singleloop wire and capacitor element. A detection device is utilized tolocate the tag by pulsed emission of a wide-band transmission signal.The tag resonates with a radiated signal, in response to the wide-bandtransmission, at its own single non-predetermined frequency, within thewide-band range. The return signals build up in intensity at a single(though not predefined) detectable frequency over ambient noise, so asto provide recognizable detection signals.

U.S. Pat. No. 5,325,873, to Hirschi et al., whose disclosure isincorporated herein by reference, describes a system to verify thelocation of a tube or other object inserted into the body. Itincorporates a resonant electrical circuit attached to the object whichresonates upon stimulation by a hand-held RF transmitter/receiverexternal to the body. The electromagnetic field generated due toresonance of the circuit is detected by the hand-held device, whichsubsequently turns on a series of LEDs to indicate to the user thedirection to the target. An additional visual display indicates when thetransmitter/receiver is directly above the object.

U.S. Pat. No. 6,239,724, to Doron et al., whose disclosure isincorporated herein by reference, describes a telemetry system forproviding spatial positioning information from within a patient's body.The system includes an implantable telemetry unit having (a) a firsttransducer, for converting a power signal received from outside the bodyinto electrical power for powering the telemetry unit; (b) a secondtransducer, for receiving a positioning field signal that is receivedfrom outside the body; and (c) a third transducer, for transmitting alocating signal to a site outside the body, in response to thepositioning field signal.

U.S. Pat. No. 6,332,089, to Acker et al., whose disclosure isincorporated herein by reference, describes a medical probe such as acatheter, which is guided within the body of a patient by determiningthe relative positions of the probe relative to another probe, forexample by transmitting nonionizing radiation to or from fieldtransducers mounted on both probes. In one embodiment, a site probe issecured to a lesion within the body, and an instrument probe fortreating the lesion may be guided to the lesion by monitoring relativepositions of the probes. Two or more probes may be coordinated with oneanother to perform a medical procedure.

Passive sensors and transponders, fixed to implanted devices, can alsobe used for conveying other diagnostic information to receivers outsidethe body. For example, U.S. Pat. No. 6,053,873, to Govari et al., whosedisclosure is incorporated herein by reference, describes a stentadapted for measuring a fluid flow in the body of a subject. The stentcontains a coil, which receives energy from an electromagnetic fieldirradiating the body so as to power a transmitter for transmitting apressure-dependent signal to a receiver outside the body. In oneembodiment, the transmitter is based on a tunnel diode oscillatorcircuit, suitably biased so as to operate in a negative resistanceregime, as is known in the art.

As another example, U.S. Pat. No. 6,206,835 to Spillman et al., whosedisclosure is incorporated herein by reference, describes an implantdevice that includes an integral, electrically-passive sensing circuit,communicating with an external interrogation circuit. The sensingcircuit includes an inductive element and has a has afrequency-dependent variable impedance loading effect on theinterrogation circuit, varying in relation to the sensed parameter.

SUMMARY OF THE INVENTION

It is an object of some aspects of the present invention to providemethods and systems for guidance of medical procedures.

In preferred embodiments of the present invention, a wireless tag isimplanted in a patient's body to mark the location of a planneddiagnostic or therapeutic procedure. During the procedure, the region ofthe body under treatment is irradiated with electromagnetic radiation(typically radio frequency—RF—radiation) or ultrasonic radiation,causing the tag to return energy indicative of its location. The energyreturned from the tag is detected by a receiver in order to determinethe location and orientation of a therapeutic or diagnostic device, suchas a surgical probe, relative to the tag. The radiation source and thereceiver for detecting the returned energy may be integrated into thetherapeutic or diagnostic device, or they may alternatively be containedin one or more separate units. In the latter case, when the receiver isseparate from the therapeutic or diagnostic device, the receiver ispreferably also capable of determining the position and orientation ofthe device.

The location and orientation of the therapeutic or diagnostic devicerelative to the tag within the body are shown on a display, for use bythe treating physician in guiding the device to the appropriatelocation. In some preferred embodiments of the present invention, thedisplay is integrated in a single unit with the therapeutic ordiagnostic device that must be guided, for example, on a handle of thedevice. The operator is thus able to guide the device while looking onlyat the tool and the region under treatment, without having to look awaytoward a separate display as in systems known in the art.

Various different types of wireless tags may be used for the purposes ofthe present invention. Preferably, the tag is passive, in the sense thatit contains no internal energy source, but rather derives all the energythat it needs to operate from the applied electromagnetic or ultrasonicradiation. Exemplary passive tags are described in the above-mentionedU.S. patent application Ser. No. 10/029,595 and in U.S. patentapplication Ser. No. 10/029,473, filed Dec. 21, 2001, which is assignedto the assignee of the present patent application and whose disclosureis likewise incorporated herein by reference. Other types of tags, asare known in the art, may also be used.

Systems and methods in accordance with embodiments of the presentinvention present invention are particularly useful in guiding biopsiesand other invasive procedures performed on soft tissues, such as thebreasts, lungs and gastrointestinal tract. Implantation of a passive tagcan be used both to provide initial guidance to the location of asuspected lesion and to provide further guidance to return to the samelocation in subsequent treatment and follow-up. Such guidance systemsmay also be used in non-invasive therapies, such as focused radiotherapyand ultrasound, to focus high-intensity radiation from a source outsidethe body onto the precise location of a lesion. Other applications willbe apparent to those skilled in the art.

There is therefore provided, in accordance with a preferred embodimentof the present invention, apparatus for performing a medical procedureon a tissue within a body of a subject, including:

-   -   a wireless tag configured to be fixed to the tissue and adapted        to emit radiation, thereby causing first signals to be generated        indicative of a location of the tag in the body;    -   an invasive medical tool, including:        -   a probe, which is adapted to penetrate into the body so as            to reach the tissue;        -   a handle, fixed proximally to the probe, and adapted to be            manipulated by an operator of the tool; and        -   a display, mounted on the handle, and adapted to present a            visual indication to the operator of an orientation of the            probe relative to the tag; and    -   a processing unit, coupled to process the first signals so as to        determine coordinates of the tag relative to the probe, and to        drive the display responsive to the coordinates.

Preferably, the invasive medical tool further includes a receiver, whichis adapted to receive the radiation emitted by the wireless tag, and togenerate the first signals responsive thereto for processing by theprocessing unit.

Further preferably, the invasive medical tool includes a tool positionsensor, which is adapted to generate second signals indicative of thecoordinates of the probe, and the processing unit is coupled to processthe second signals together with the first signals so as to determinethe coordinates of the tag relative to the probe. In a preferredembodiment, the apparatus includes one or more field generators, whichare fixed in the external frame of reference and which are adapted togenerate electromagnetic fields in a vicinity of the tissue, and thewireless tag and the tool position sensor include field sensors, inwhich electrical currents flow responsive to the electromagnetic fields,and wherein the first and second signals are indicative of theelectrical currents flowing in the field sensors.

Preferably, the radiation emitted by the tag includes radio-frequency(RF) electromagnetic radiation. In a preferred embodiment, the apparatusincludes one or more acoustic transmitters, which are adapted totransmit acoustic energy into the body in a vicinity of the tissue, andwherein the tag is adapted to receive and use the acoustic energy ingenerating the electromagnetic radiation.

Alternatively, the radiation emitted by the tag includes acousticradiation.

Preferably, the display is adapted to present a further visualindication of a distance from the probe to the tag.

In a preferred embodiment, the invasive medical tool is adapted toperform a surgical procedure on the tissue. Additionally oralternatively, the invasive tool includes an endoscope.

There is also provided, in accordance with a preferred embodiment of thepresent invention, a method for performing a medical procedure on atissue within a body of a subject, including:

-   -   fixing a wireless tag to the tissue;    -   actuating the tag to emit radiation, thereby causing first        signals to be generated indicative of a location of the tag in        the body;    -   introducing an invasive medical tool into the body by        manipulating a handle of the tool;    -   processing the first signals so as to determine coordinates of        the tag relative to the tool;    -   responsive to the coordinates, displaying a visual indication on        the handle of the tool of an orientation of the tool relative to        the tag; and    -   advancing the tool into the body to the tissue by manipulating        the handle while observing the visual indication so that the        tool reaches the tissue.

The present invention will be more fully understood from the followingdetailed description of the preferred embodiments thereof, takentogether with the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial illustration showing a partly-cutawayview of an implantable passive tag, in accordance with a preferredembodiment of the present invention;

FIG. 2 is a schematic, pictorial illustration showing a surgical probethat is guided to the location of a passive tag in the breast of asubject using a display on the probe, in accordance with a preferredembodiment of the present invention;

FIG. 3 is a flow chart that schematically illustrates a method forcarrying out an invasive medical procedure on body tissue using a tagimplanted in the tissue, in accordance with a preferred embodiment ofthe present invention;

FIG. 4 is a schematic, pictorial illustration showing a partly-cutawayview of an implantable passive tag, in accordance with another preferredembodiment of the present invention;

FIG. 5 is a schematic electrical diagram of a passive tag, in accordancewith a preferred embodiment of the present invention;

FIG. 6 is a schematic, pictorial illustration of a system for guiding asurgical probe to the location of a passive tag in the breast of asubject, in accordance with a preferred embodiment of the presentinvention;

FIG. 7 is a schematic, pictorial illustration of a system for guiding asurgical probe to the location of a passive tag in the breast of asubject, in accordance with another preferred embodiment of the presentinvention;

FIG. 8 is a flow chart that schematically illustrates a method forcarrying out an invasive medical procedure on body tissue using a tagimplanted in the tissue, in accordance with a preferred embodiment ofthe present invention;

FIG. 9 is a schematic, pictorial illustration showing a cutaway view ofan ultrasonic reflecting tag, in accordance with a preferred embodimentof the present invention;

FIG. 10 is a schematic, pictorial illustration of a system for guiding asurgical probe to the location of a passive tag in the breast of asubject, in accordance with still another preferred embodiment of thepresent invention;

FIG. 11 is a flow chart that schematically illustrates a method forcarrying out an invasive medical procedure on body tissue using a tagimplanted in the tissue, in accordance with a preferred embodiment ofthe present invention;

FIG. 12 is a schematic, pictorial illustration showing an endoscope thatis guided to the location of a passive tag in the lung of a subjectusing a display on the endoscope, in accordance with a preferredembodiment of the present invention; and

FIG. 13 is a schematic, pictorial illustration of a system for guidingan endoscope to the location of a passive tag in the colon of a subject,in accordance with still another preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic, pictorial illustration that shows apartly-cutaway view of an implantable passive tag 20, in accordance witha preferred embodiment of the present invention. Tag 20 of the typeshown and described here is also referred to herein as a “beacon.” Thetag comprises a RF antenna 22, typically having the form of a coil,which is coupled to a capacitor 24 and additional circuitry 26 to definea resonant circuit. The coil, capacitor and circuitry are contained in asealed, biocompatible package 28, typically made of a plastic or othernon-conducting material. In the embodiment pictured in FIG. 1, package28 includes a base that can be grasped by a radiologist using a suitableinserter tool (not shown in the figures) to position tag 20 at a desiredlocation in soft tissue of a patient.

Preferably, circuitry 26 comprises a tunnel diode (not shown), such as a1n3712 diode, which is configured together with antenna 22 and capacitor24 to form a tunnel diode oscillator circuit, as is known in the art.For example, the antenna may be formed by a small loop of 0.5 mm wire,and coupled to a 40 pF capacitor. Further details of the design of atunnel diode oscillator circuit and its use in a wireless transponderare described in the above-mentioned U.S. Pat. No. 6,053,873. In brief,the oscillator circuit is excited by an externally-generatedelectromagnetic field at a first frequency (f1), which causes theoscillator circuit to radiate a response field at another frequency(f2). Tunnel diodes are particularly well suited for this purpose,because the characteristic I-V curve of a tunnel diode includes aportion in which the diode demonstrates “negative” resistance, i.e., asthe voltage applied across the diode decreases, the current through thediode increases, causing oscillations to occur in the circuit. Theoscillation frequency (f2) differs from the normal resonant frequency ofthe circuit because of the effective capacitance of the tunnel diode.Typically, frequency f2 differs from the excitation frequency f1 byabout 10%-40%. For example, an excitation frequency f1 of 88 MHz mayyield a response field having a frequency f2 of 120 MHz. The intensityand direction of the response field can be used to “home in” on thelocation of tag 20, as described below. Alternatively, other types ofre-radiating oscillators may be used for this purpose, as well.

FIG. 2 is a schematic, pictorial illustration showing implantation oftag 20 in a breast 30 of a patient, and its use in guiding a surgicaltool 32, in accordance with a preferred embodiment of the presentinvention. Typically, tool 32 comprises a probe 34, which is used, forexample, to cut and extract a biopsy sample from breast 30 at thelocation marked by tag 20. Tool 32 comprises an antenna assembly 36,which is coupled to excitation and detection circuitry, contained eitherwithin tool 32 or in a separate processing unit (not shown in thisfigure). Antenna assembly 36 is driven to radiate RF energy at or nearthe excitation frequency f1 of the circuitry in tag 20. This excitationenergy causes the tag to radiate a response field at frequency f2, whichis detected by the antenna assembly. Typically, antenna assembly 36comprises two or more antennas (not shown), spaced around thelongitudinal axis of probe 34. The difference between the respectivefield strengths sensed by the antennas at frequency f2 is indicative ofthe direction and magnitude of the misalignment of the probe axisrelative to the location of tag 20. Based on the detected responsefields, a display 38 on the handle of tool 32 guides the surgeon indirecting probe 34 precisely to the location of tag 20. When the signalsfrom the antennas are equal, the probe axis is aligned with the tag.

FIG. 3 is a flow chart that schematically illustrates a method forperforming a surgical procedure using tag 20 and tool 32, in accordancewith a preferred embodiment of the present invention. The tag isinitially implanted in breast 30 by a radiologist, at an implant step40. This step is typically carried out while imaging the breast todetermine the location of a suspicious lesion, so as to place tag 20within or adjacent to the lesion. A surgeon then brings probe 34 intoproximity with breast. Antenna assembly 36 transmits a RF field in thedirection of probe 34, toward breast 30, at a power transmission step42. As noted above, the transmitted field is at or near the excitationfrequency of the oscillator circuit in tag 20. The oscillation thusengendered in the circuit causes it to radiate a response field, orbeacon signal, at a beacon transmission step 44.

Antenna assembly 36 receives the beacon signal, at a beacon receptionstep 46, and the signal is processed to measure its strength and,optionally, its directional characteristics. These characteristics areused in driving display 38 to give the surgeon a visual indication ofhow probe 34 should be directed through the breast tissue in order toreach tag 20. In one embodiment, display 38 simply gives a signalstrength indication, and the surgeon directs the probe so as to maximizethe signal strength. In another embodiment, the response signal isprocessed to generate a directional signal, typically using multipleantennas in assembly 36, as described above. The antenna outputs areprocessed, using analog and/or digital differential processingcircuitry, to drive a pointer or cursor on display 38, indicating thedirection from probe 34 to tag 20. Optionally, tool 32 also provides anaudible indication, such as a tone or sequence of tones, to cue thesurgeon as to whether or not the probe is correctly directed to thetarget in breast 30.

The surgeon uses the information provided by display 38 to guide probe34 toward tag 20, at a guidance step 48. Steps 42 through 48 arerepeated continually until the distal tip of probe 34 reaches thelocation of tag 20, at a success step 50. Successful penetration by theprobe tip to the tag location can be determined in a number of differentways. For example, an antenna or other sensor may be incorporated in theprobe near its distal tip in order to signal when the probe contacts thetag. Alternatively, each of the multiple antennas in assembly 36 can beused to find a respective directional vector, pointing from the antennato the tag location. The crossing point of these vectors indicates thelocation of the tag. It is thus determined that the probe tip hasreached the tag location when the distance from antenna assembly 36 tothe vector crossing point is equal to the known length of probe 34. Atthis point, display 38 preferably gives an indication of success, suchas a change in color or audible signal. The surgeon can then completethe biopsy or other procedure that is warranted. Tag 20 may either besurgically removed as part of this procedure, or it may be left in placefor future access.

FIG. 4 is a schematic, pictorial illustration that shows apartly-cutaway view of an implantable passive tag 54, in accordance withanother preferred embodiment of the present invention. Tag 54 comprises,in addition to antenna 22, one or more position-sensing coils 56.Application of electromagnetic fields to coils 56 by external fieldgenerators causes currents to flow in these coils. The amplitudes of thecurrents can be used to determine the position and orientationcoordinates of the coils relative to the field generators (as shownbelow in FIG. 6). Exemplary methods for determining position andorientation of an invasive device using coils such as these aredescribed in U.S. Pat. No. 5,391,199, to Ben-Haim, and in U.S. patentapplication Ser. No. 08/793,371 filed May 14, 1997 (PCT PatentPublication WO 96/05768, to Ben-Haim et al.), whose disclosures areincorporated herein by reference. Three position-sensing coils 56 can beused to provide six-dimensional location and orientation coordinates oftag 54. For applications that do not require full, six-dimensionalinformation, a single position-sensing coil is adequate.

Coils 56 are coupled to control circuitry 58, which senses the currentsflowing in the coils for use in determining the coordinates of tag 54.Preferably, circuitry 58 generates signals in which the currentmagnitudes are encoded and causes these signals to be transmitted byantenna 22. The signals are decoded and processed by an externalprocessing unit to determine the coordinates of the tag. Optionally, tag54 may also comprise one or more additional sensors 60, which measurephysiological parameters at the site of the tag in the body. Examples ofsuch sensors include temperature sensors, pressure sensors, pH sensors,and other sensors for measuring physical and chemical properties oftissues with which tag 54 is in contact. Circuitry 58 encodes andtransmits these sensor measurements, as well.

FIG. 5 is an electrical schematic diagram showing circuit elements oftag 54, in accordance with a preferred embodiment of the presentinvention. Antenna 22 is preferably optimized to receive and transmithigh-frequency signals, in the range above 1 MHz. Coil 56, on the otherhand, is preferably designed for operation in the range of 1-3 kHz, atwhich the external field generators generate their electromagneticfields. Alternatively, other frequency ranges may be used, as dictatedby application requirements. According to this embodiment, tag 54 cantypically be made about 2-5 mm in length and 2-3 mm in outer diameter.Further aspects of this type of tag are described in the above-mentionedU.S. patent application Ser. No. 10/029,473.

To determine the position of tag 54, electric fields are applied to thearea of the patient's body containing the tag by a number of fieldgenerators in different, known positions and/or orientations.Preferably, each of the field generators has its own, distinct operatingfrequency. Control circuitry 58 measures the currents flowing in sensorcoil 56 at the different field frequencies and encodes the measurementsin a high-frequency signal transmitted via antenna 22. Alternatively oradditionally, the different field generators are time-multiplexed, eachoperating during its own preassigned time slots.

In the embodiment pictured in FIG. 5, circuitry 58 comprises avoltage-to-frequency (V/F) converter 62, which generates a RF signalwhose frequency is proportional to the voltage produced by the sensorcoil current flowing across a load. Preferably, the RF signal producedby circuitry 58 has a carrier frequency in the 50-150 MHz range. The RFsignal produced in this manner is modulated with a number of differentfrequency modulation (FM) components that vary over time at therespective frequencies of the fields generated by the field generators.The magnitude of the modulation is proportional to the currentcomponents at the different frequencies. A receiver outside thepatient's body demodulates the RF signal to determine the magnitudes ofthe current components and thereby to calculate the coordinates of tag54.

Alternatively, circuitry 58 may comprise a sampling circuit andanalog/digital (A/D) converter (not shown in the figures), whichdigitizes the amplitude of the current flowing in sensor coil 56. Inthis case, circuitry 58 generates a digitally-modulated signal, andRF-modulates the signal for transmission by antenna 22. Any suitablemethod of digital encoding and modulation may be used for this purpose.Other methods of signal processing and modulation will be apparent tothose skilled in the art.

FIG. 6 is a schematic, pictorial illustration of a system 66 for guidinga surgical tool 76 to the location of tag 54 in breast 30, in accordancewith a preferred embodiment of the present invention. A power coil 68generates a high-frequency RF field, preferably in the 2-10 MHz range.This field causes a current to flow in antenna 22, which is rectified bycircuitry 58 and used to power its internal circuits. Meanwhile, fieldgenerator coils 70 produce electromagnetic fields, preferably in the 1-3kHz range, which cause currents to flow in sensor coil (or coils) 56.These currents have frequency components at the same frequencies as thedriving currents flowing through the generator coils. The currentcomponents are proportional to the strengths of the components of therespective magnetic fields produced by the generator coils in adirection parallel to the sensor coil axis. Thus, the amplitudes of thecurrents indicate the position and orientation of coil 56 relative tofixed generator coils 70.

Circuitry 58 encodes the current amplitudes from coil 56 into ahigh-frequency signal, which is transmitted by antenna 22.Alternatively, tag 54 may comprise separate antennas for receiving RFpower and for transmitting signals, as described, for example, in theabove-mentioned U.S. Pat. No. 6,239,724. The encoded signal is receivedby coil 68 or by another receiving antenna, and is conveyed to aprocessing unit 72. Typically, processing unit 72 comprises ageneral-purpose computer, with suitable input circuits and software forprocessing the position signals received over the air from tag 54. Theprocessing unit computes position and, optionally, orientationcoordinates of tag 54, and then shows the tag coordinates on a display74.

Surgical tool 76 also comprises a position sensor 78, comprising one ormore coils similar in form and function to coils 56 in tag 54. Thefields produced by field generator coils 70 also cause currents to flowin sensor 78, in response to the position and orientation of tool 76relative to coils 70. The current signals thus produced are alsoconveyed to processing unit 72, either over the air, as in the case oftag 54, or via wire. If sensor 78 transmits the signals over the air, itpreferably uses a different carrier frequency from that of tag 54 sothat the signals can be easily distinguished one from another.

Based on the signals from tag 54 and from sensor 78, processing unit 72computes the position and orientation of tool 76 relative to thelocation of the tag in breast 30. A pointer and/or cursor is shown ondisplay 74 to indicate to the surgeon whether the tool is aimed properlytowards its target. Various methods of coordinate display may be usedfor this purpose, such as a three-dimensional grid mesh, atwo-dimensional grid, a two- or-three dimensional polar representation,numerical coordinate readout, or other methods known in the art.Optionally, the positions of the tag and tool are registered, usingtheir measured positions and orientations, with an image of breast 30,such as an X-ray, CT or ultrasound image. The image of the breast isshown on display 74, and icons corresponding to the positions of the tagand the tool are superimposed on the image. Further methods of displaythat are useful in image-guided surgery are described in theabove-mentioned U.S. Pat. No. 6,332,098.

FIG. 7 is a schematic, pictorial illustration of a system 80 for guidingsurgical tool 76 to the location of a tag 81 in breast 30, in accordancewith another preferred embodiment of the present invention. In thisembodiment, a tag 81 receives its operating power not from anelectromagnetic field (such as that of coil 68), but from acousticenergy generated by an ultrasound transmitter 82. A tag of this sort isshown, for example, in the above-mentioned U.S. patent application Ser.No. 10/029,595. The acoustic energy generated by transmitter 82 excitesa miniature transducer, such as a piezoelectric crystal, in tag 81, togenerate electrical energy. The electrical energy causes a current toflow in one or more coils in tag 81, such as coil 56 described above.The currents in the coils in tag 81 generate electromagnetic fieldsoutside breast 30, which are in this case received by coils 70 (nowacting as field receivers, rather than field generators). The amplitudesof the currents flowing in coils 70 at the frequency of the appliedacoustic energy are measured to determine the position of tag 81.

Alternatively, tag 81 may be similar in operation to tag 54, in thatsensor coil or coils 56 in the tag receive a field generated by coils70, and then circuitry in the tag transmits a signal indicating theamplitudes of the current components in coils 56. In the embodiment ofFIG. 7, however, the circuitry in the tag receives power not from coil68, but rather by rectifying the electrical energy generated by thepiezoelectric crystal (or other transducer) in tag 81 in response to theacoustic energy applied by transmitter 82. The tag may transmit itssignal in pulses, rather than continuously, and a capacitor may be usedto store energy in tag 81 in the intervals between the pulses, so thatthe transmitted signal is powerful enough to be received outside thebody with good signal/noise ratio.

As in the preceding embodiment, sensor 78 is used to determine theposition and orientation of tool 76. Sensor 78 may either receive thefields generated by coils 70, as described above, or it may be driven togenerate fields, which are received by coils 70.

The position signals generated by tag 81 and sensor 78 are received andprocessed by a combined location pad and display unit 84. This unittakes the place of the separate processing unit 72, coils 70 and display74 used in the preceding embodiment. Unit 84 is preferably held by astable, movable mount (not shown), enabling the surgeon to place theunit in proximity to breast 30 and in a position in which a display 86on the unit can be viewed conveniently. Field generator coils 70 arebuilt into unit 84, so that the positions of tag 81 and tool 76 aredetermined relative to the unit. (Coils 70 are seen in the figure incutaway view, but ordinarily would be contained inside the case of theunit, protected by a non-conductive cover.) Since it is not the absolutepositions of tag 81 and tool 76 that are of concern, but rather theirrelative positions and orientations, the surgeon may move unit 84 duringthe surgery as required, in order to ensure that the signals from tag 81and sensor 78 are sufficiently strong, that display 86 is easilyvisible, and that the unit itself does not interfere with the surgeon'swork.

Display 86 preferably comprises a distance guide 88 and an orientationtarget 92. A mark 90 on distance guide 88 indicates how far the tip oftool 76 is from the location of tag 81. A cursor 94 on target 92indicates the orientation of tool 76 relative to the axis required toreach the location of tag 81. When the cursor is centered on the target,it means that tool 76 is pointing directly toward tag 81. Display 38(FIG. 2) preferably works on a similar principle.

FIG. 8 is a flow chart that schematically illustrates a method forperforming a surgical procedure using system 80, including tag 81 andcombined location pad and display unit 84, in accordance with apreferred embodiment of the present invention. A similar procedure maybe carried out, mutatis mutandis, using the elements of system 66, shownin FIG. 6. As described above with reference to FIG. 3, the procedurebegins with implantation of the appropriate tag at the target locationin breast 30, at an implant step 100. The tag is then energized byapplying transmitter 82 to the breast, and driving the transmitter togenerate acoustic energy, at an energizing step 102. Alternatively, iftag 54 is used, coil 68 is used to energize the tag with RF power.

Energizing the tag causes it to transmit a location signal to unit 84,at a tag transmission step 104. At the same time, or in alternation withthe tag transmission, sensor 78 conveys a location signal to unit 84, aswell, at a tool transmission step 106. Unit 84 (or processing unit 72,in the embodiment of FIG. 6) receives the location signals anddetermines the relative coordinates of tool 76 and tag 81, at acoordinate determination step 108. Based on this determination, thelocation and orientation of the tool relative to the tag are shown ondisplay 86 in the manner described above.

The surgeon uses the information presented by display 86 to guide thedistal end of tool 76 to the location of tag 81, at a probe guidancestep 110. In typical operation, the surgeon holds the tool at a selectedstarting position and aims it toward tag 81, using target 92. Thesurgeon then advances the tool into breast 30, keeping cursor 94centered on target 92. Steps 102 through 110 are repeated continuallyuntil mark 90 indicates that the tool has reached the location of tag81, at a success step 112. The biopsy or other desired procedure canthen be performed.

FIG. 9 is a schematic, pictorial, partly-cutaway illustration of anultrasonic reflecting tag 120, in accordance with another preferredembodiment of the present invention. Various tags of this sort, whichare applicable to the purposes of the present invention, are shown anddescribed in the above-mentioned U.S. patent application Ser. No.10/029,595. Tag 120 in the present embodiment has the form of aspherical bubble, comprising a shell 122 that is struck by ultrasoundwaves generated by acoustic transducers outside the patient's body. Theincident ultrasound waves induce the tag to resonate and to emit adetectable ultrasound echo. If shell 122 is spherical (as shown), thenthe emitted echo is generally isotropic, and triangulation of the echocan yield the location of the target in the body.

Preferably, shell 122 contains a medium 124, and the shell and mediumare configured so that tag 120 has a nonlinear vibrational response toincident ultrasonic radiation. Ultrasound waves having a frequency f1,emitted by the acoustic generators outside the patient's body, strikethe shell, imparting energy to the shell and/or the contained medium.The shell then emits ultrasound waves at its resonant frequency f2,which is different from f1. The resonant frequency is determined byparameters such as the shell radius, Young modulus and thickness, as isknown in the art. Preferably, to generate strong echoes, the designparameters of tag 120 and the excitation frequency f1 are chosen so thatf2 is a multiple of f1.

FIG. 10 is a schematic, pictorial illustration showing a system 125 forguiding surgical tool 76 to the location of tag 120 in breast 30, inaccordance with a preferred embodiment of the present invention. Thisembodiment also uses the combined location pad and display unit 84described above. Multiple ultrasonic transducers 126 are applied tobreast 30. Each transducer in turn is driven to generate a pulse ofultrasonic energy at frequency f1, and then to detect the echo signalreturned by tag 120 at frequency f2. Alternatively or additionally, allthe transducers may detect the echo returned due to the ultrasonicpulses generated by a single one of the transducers. The time delaybetween generation of the ultrasonic pulse and receipt of the echoindicates the distance from each of transducers 126 to tag 120.Alternatively or additionally, the power of the echo signal received byeach of transducers 126 may be used to determine the distances.

To determine the actual location of tag 120 in breast 30, however, it isnecessary to know the locations of transducers 126. For this purpose, asensor coil 128 is attached to each of the transducers. Energizing fieldgenerator coils 70 in unit 84 causes currents to flow in sensor coils128. The amplitudes of these currents, as noted above, depend on thelocations and orientations of the sensor coils relative to the fieldgenerator coils. Unit 84 analyzes the currents flowing in sensor coils128 in order to determine the position coordinates of transducers 126.Based on these coordinates, along with the distances measured byultrasound reflection from each of transducers 126 to tag 120, unit 84is able to determine the exact location of the tag in a fixed, externalframe of reference.

The location and orientation coordinates of tool 76 relative to unit 84are determined using sensor 78, as described above, so that the distanceand direction from the tool to tag 120 can also be calculated anddisplayed.

It will be observed that system 125 uses two sets of positionmeasurements to find the location of tag 120: location of transducers126 relative to unit 84, and location of tag 120 relative to thetransducers. This added level of complication is not present in theembodiments described earlier. On the other hand, by comparison withtags 20, 54 and 81, tag 120 is extremely simply and inexpensive tofabricate and can be made very small if desired. Typically, tag 120 hasa diameter less than 2 mm.

FIG. 11 is a flow chart that schematically illustrates a method forperforming a surgical procedure using system 125, including tag 120, inaccordance with a preferred embodiment of the present invention. In thisembodiment, too, the procedure starts with implantation of tag 120 by aradiologist at the site of a suspected lesion in breast 30, at animplant step 130. Preferably, for this purpose, the material of shell122 is selected so as to be clearly visible using standard imagingtechniques. Then, in preparation for surgery, transducers 126 are fixedto the skin of breast 30 around the location of tag 120, at a transducerfixation step 132.

In order to find the relative positions and orientations of tool 76 andtransducers 126, field generator coils 70 are actuated, and the currentsflowing in sensor 78 and sensor coils 128 are measured, at a RF locationstep 134. Alternatively, other position sensing techniques may be usedfor this purpose. For example, optical sensing techniques may be used tofind the coordinates of tool 76 and of transducers 126 at step 134,since both tool 76 and transducers 126 are outside the patient's body.Ultrasonic position sensing techniques may likewise be used.

Transducers 126 are actuated, and the echoes received by the transducersfrom tag 120 are measured, at an echo measurement step 136. The echoesare used to determine the distance from each of transducers 126 to tag120, as described above. (The order of steps 134 and 136 mayalternatively be reversed.) Unit 84 then performs the necessarygeometrical calculations and transformations to find the position andorientation of tool 76 relative to tag 120, at a triangulation step 138.The distance of the tool from the tag and the orientation of the toolrelative to the direct approach axis to the tag are shown on display 86,at a display step 140, as described above.

The surgeon uses the information presented by display 86 to guide thedistal end of tool 76 to the location of tag 120, at a probe guidancestep 142. The surgeon advances the tool into breast 30, keeping cursor94 centered on target 92, as described above. Steps 134 through 142 arerepeated continually until mark 90 indicates that the tool has reachedthe location of tag 81, at a success step 144. The biopsy or otherdesired procedure can then be performed.

Although the preferred embodiments described above all relate to breastsurgery, and particularly to breast biopsy, the devices and methods usedin these embodiments may also be adapted to other procedures and totreatment of other body organs. For example, tags such as thosedescribed above may be implanted in body tissues to be treated byhigh-intensity focused radiation. Such techniques are typically used forablation of tumors and other lesions inside the body. In therapeuticapplications of this sort, the radiologist would implant the tag at thelocation to be treated, and the radiation sources to be used for thetreatment would then be aimed at the tag location. Referring again toFIG. 10, for instance, if transducers 126 were of a type suitable to beused in high-intensity focused ultrasound (HIFU) treatment, they couldbe oriented and aimed toward the location of tag 120 using the positionsignals and display generated by unit 84.

FIG. 12 is a schematic, pictorial illustration showing the use of tag 20in a bronchoscopy procedure, in accordance with a preferred embodimentof the present invention. Tag 20 is fixed to a suspicious nodule 154,which was discovered during an imaging procedure performed in a lung 150of a patient 152. A bronchoscope 156 is used to inspect and, possibly,to biopsy nodule 154. It is also desirable to be able to return easilyto the same nodule location for follow-up in subsequent bronchoscopicexaminations. A physician 157 operates bronchoscope 156 by grasping andmanipulating a handle 158. Bronchoscope comprises elements similar totool 32 shown in FIG. 2: antenna assembly 36 (suitably adapted andminiaturized) at the distal end of the bronchoscope, and display 38 onhandle 158. While viewing the display, physician 157 turns a steeringknob 160 and advances the bronchoscope into lung 150 until it reachesthe location of nodule 154.

Although this embodiment is based on tag 20, as shown in FIG. 1, theother RF-based tags described above (such as tag 54 shown in FIG. 4) mayalso be used for this purpose. Tags based on the use of ultrasound, onthe other hand, are typically less satisfactory for pulmonaryapplications.

FIG. 13 is a schematic, pictorial illustration showing the use of tag120 in a colonoscopy procedure, in accordance with a preferredembodiment of the present invention. In this example, tag 120 is fixedto a polyp 164 that was discovered in a colon 162 of a patient.Ultrasound transducers 126 (as shown in FIG. 10, but not in this figure)are fixed to the patient's abdomen, to enable the location of tag 120 tobe determined, in the manner described above. A colonoscope 160 isadvanced through colon 162, and its position is tracked by means ofsensor 78. As the distal end of the colonoscope approaches the locationof tag 120, unit 84 displays the distance and direction from thecolonoscope to the tag. Optionally, an icon indicating the position oftag 120 is superimposed on a video image of the interior of colon 162that is formed by an image sensor in the colonoscope and displayed on asuitable video display.

Although the preferred embodiments described above are directed tocertain specific medical and surgical procedures in particular bodyorgans, other areas of application of the tags, ancillary equipment andmethods of the present invention will be apparent to those skilled inthe art. The principles of the present invention may similarly beapplied to other types of surgery, including particularlyminimally-invasive surgery, as well as endoscopic and non-invasivetreatment and diagnostic modalities.

It will thus be appreciated that the preferred embodiments describedabove are cited by way of example, and that the present invention is notlimited to what has been particularly shown and described hereinabove.Rather, the scope of the present invention includes both combinationsand subcombinations of the various features described hereinabove, aswell as variations and modifications thereof which would occur topersons skilled in the art upon reading the foregoing description andwhich are not disclosed in the prior art.

1. Apparatus for performing a medical procedure on a tissue within a body of a subject, comprising: a wireless tag configured to be fixed to the tissue and adapted to emit radiation, thereby causing first signals to be generated indicative of location and orientation coordinates of the tag in the body; an invasive medical tool, comprising: a probe, which is adapted to penetrate into the body so as to reach the tissue; a handle, fixed proximally to the probe, and adapted to be manipulated by an operator of the tool; and a display, mounted on the handle, and adapted to present a visual indication to the operator of an orientation of the probe relative to the tag based on the location and orientation coordinates; and a processing unit, coupled to process the first signals so as to determine the location and orientation coordinates of the tag relative to the probe, and to drive the display responsive to the location and orientation coordinates.
 2. Apparatus according to claim 1, wherein the invasive medical tool further comprises a receiver, which is adapted to receive the radiation emitted by the wireless tag, and to generate the first signals responsive thereto for processing by the processing unit.
 3. Apparatus according to claim 2, wherein the radiation emitted by the tag comprises radio-frequency (RF) electromagnetic radiation.
 4. Apparatus according to claim 1, wherein the invasive medical tool further comprises a tool position sensor, which is adapted to generate second signals indicative of the location and orientation coordinates of the probe, and wherein the processing unit is coupled to process the second signals together with the first signals so as to determine the location and orientation coordinates of the tag relative to the probe.
 5. Apparatus according to claim 4, and comprising one or more field generators, which are fixed in the external frame of reference and which are adapted to generate electromagnetic fields in a vicinity of the tissue, and wherein the wireless tag and the tool position sensor comprise field sensors, in which electrical currents flow responsive to the electromagnetic fields, and wherein the first and second signals are indicative of the electrical currents flowing in the field sensors.
 6. Apparatus according to claim 1, wherein the radiation emitted by the tag comprises radio-frequency (RF) electromagnetic radiation.
 7. Apparatus according to claim 6, and comprising one or more acoustic transmitters, which are adapted to transmit acoustic energy into the body in a vicinity of the tissue, and wherein the tag is adapted to receive and use the acoustic energy in generating the electromagnetic radiation.
 8. Apparatus according to claim 1, wherein the radiation emitted by the tag comprises acoustic radiation.
 9. Apparatus according to claim 1, wherein the display is adapted to present a further visual indication of a distance from the probe to the tag.
 10. Apparatus according to claim 1, wherein the invasive medical tool is adapted to perform a surgical procedure on the tissue.
 11. Apparatus according to claim 1, wherein the invasive tool comprises an endoscope.
 12. Apparatus according to claim 1, wherein the location and orientation coordinates are six-dimensional location and orientation coordinates.
 13. A method for performing a medical procedure on a tissue within a body of a subject, comprising: fixing a wireless tag to the tissue; actuating the tag to emit radiation, thereby causing first signals to be generated indicative of location and orientation coordinates of the tag in the body; introducing an invasive medical tool into the body by manipulating a handle of the tool; processing the first signals so as to determine the location and orientation coordinates of the tag relative to the tool; responsive to location and orientation the coordinates, displaying a visual indication on the handle of the tool of an orientation of the tool relative to the tag; and advancing the tool into the body to the tissue by manipulating the handle while observing the visual indication so that the tool reaches the tissue.
 14. A method according to claim 13, wherein processing the first signals comprises receiving the radiation emitted by the wireless tag using a receiver in the medical tool, and generating the first signals responsive to the received radiation.
 15. A method according to claim 14, wherein receiving the radiation emitted by the tag comprises receiving radio-frequency (RF) electromagnetic radiation.
 16. A method according to claim 13, and comprising receiving second signals generated by a tool position sensor coupled to the invasive medical tool, indicative of the location and orientation coordinates of the tool, and wherein processing the first signals comprises processing the second signals together with the first signals so as to determine the location and orientation coordinates of the tag relative to the probe.
 17. A method according to claim 16, wherein actuating the tag comprises generating electromagnetic fields in a vicinity of the tissue, and wherein the wireless tag and the tool position sensor comprise field sensors, in which electrical currents flow responsive to the electromagnetic fields, and wherein the first and second signals are indicative of the electrical currents flowing in the field sensors.
 18. A method according to claim 12, wherein actuating the tag comprises actuating the tag to emit radio-frequency (RF) electromagnetic radiation.
 19. A method according to claim 18, wherein actuating the tag to emit RF electromagnetic radiation comprises transmitting acoustic energy into the body in a vicinity of the tissue, wherein the tag receives and uses the acoustic energy in generating the electromagnetic radiation.
 20. A method according to claim 13, wherein actuating the tag comprises actuating the tag to emit acoustic radiation.
 21. A method according to claim 13, and comprising displaying a further visual indication of a distance from the probe to the tag.
 22. A method according to claim 13, wherein advancing the tool into the body comprises performing a surgical procedure on the tissue.
 23. A method according to claim 1, wherein advancing the tool into the body comprises performing an endoscopic procedure on the tissue.
 24. A method according to claim 13, further comprising determining six-dimensional location and orientation coordinates of the tag relative to the tool. 